1. Field of the Invention
The present invention relates to a method and a related apparatus for selecting an audio data source for a multimedia device, and more particularly, to a method and a related apparatus for switching to the audio data source according to a number of errors in the audio data.
2. Description of the Prior Art
A television is an important part of modern life. With the advancement of technology, the video and audio quality of televisions improves accordingly. Common audio standards for television broadcasting systems, such as A2/NICAM (Near Instantaneous Companded Audio Multiplex) in Europe, BTSC in North America, and EIA-J in Japan, are different from each other. A television broadcasting transmitter performs an analog modulation as AM/FM or a digital modulation as QPSK on audio data, for generating analog/digital modulated signals, and transmits analog/digital modulated signals to an end user, i.e. a television. Next, the television performs demodulation on received audio signals according to the selected audio standard and plays the audio data.
Analog modulated signals are often accompanied by noise that is difficult to cancel during transmission, which results in a bad audio quality. Noise cancellation for digital modulated signals, however, is easy to do because digital modulated signals are protected by an encoding process, and therefore an audio quality of digital modulated signals is usually better than that of analog modulated signals. The audio quality of digital modulated signals declines much more quickly, however, when a signal quality is worse than an acceptable level. In this situation, a television user may hear an uncomfortable “popping” noise when playing the audio data demodulated from digital modulated signals of bad signal quality.
For a television using A2/NICAM standard, audio data sources of the television include a digital source for playing digital modulated signals and an analog source for playing analog modulated signals. When a signal quality is worse than the acceptable level, the television switches an audio data source from the digital source to the analog source or to a mute mode. A prior art method for switching an audio data source periodically detects a bit error rate (BER) of audio signals via a timer and compares the BER with a threshold. When the BER is higher than the threshold, the television switches from the digital source to the analog source or to a mute mode, for avoiding the popping noise.
The prior art method cannot be used to switch to the appropriate audio data source in time, however, because the television detects the BER periodically. When the signal quality declines quickly between two detecting points, the television does not switch from the digital source to the analog source and the television user will hear the popping noise. Thus the audio quality of the television declines.